1. Field of the Invention
The invention concerns a method and a control sequence determination device to determine a magnetic resonance system control command sequence to acquire raw magnetic resonance data for a magnetic resonance measurement sequence that includes a number of individual measurements in order to evaluate the individual measurements later with regard to an evaluation parameter, and to combine the overall evaluation result that is thereby obtained from the individual measurements into an overall evaluation result of the measurement. The invention furthermore concerns a method to operate a magnetic resonance system using such a control command sequence, as well as a magnetic resonance system with a corresponding control sequence determination device.
2. Description of the Prior Art
In a magnetic resonance system, the body to be examined is typically exposed to a relatively high basic magnetic field (for example of 3 or 7 Tesla) with the use of a basic magnetic field system. A magnetic field gradient is additionally applied with the aid of a gradient system. Excitation signals (RF signals) are then emitted via a radio-frequency transmission system by means of suitable antenna devices, which should lead to the effect that the nuclear spins of specific atoms excited to resonance by this radio-frequency field, are flipped by a defined flip angle relative to the magnetic field lines of the basic magnetic field. This radio-frequency excitation or the resulting flip angle distribution is also designated in the following as a nuclear magnetization, or “magnetization” for short. Upon relaxation of the nuclear spins, radio-frequency signals (magnetic resonance signals) are radiated that are received by suitable reception antennas and are then processed further. Finally, the desired image data can be reconstructed from the raw data acquired in such a manner. The emission of the radio-frequency signals or nuclear magnetic resonance magnetization for the most part takes place by the use of a “whole body coil” or “body coil”.
In order to implement a defined magnetic resonance measurement, a control command sequence is typically generated in advance, which control command sequence includes the individual RF pulses to be emitted and gradient pulses to be emitted in coordination for this. This control command sequence is defined (possibly with additional control specifications) in what is known as a measurement protocol which is created in advance and retrieved (from a memory, for example) for a defined measurement and can possibly be modified on site by the operator. During the measurement, the control of the magnetic resonance system then takes place wholly automatically on the basis of this measurement protocol, wherein the control device of the magnetic resonance system reads out and executes the commands from the measurement protocol.
In most cases, magnetic resonance examinations are composed of a sequence of multiple contiguous individual measurements. Typically, multiple parallel, equidistant slices of an examination subject are thus acquired in a multislice measurement in order to optimally acquire the entire volume of a region of interest of the examination subject. For many examinations or diagnostic questions, the individual measurements are—as already mentioned—additionally evaluated later with regard to a specific evaluation parameter, and the evaluation results that are thereby obtained from the individual measurements are combined into an overall evaluation result. A typical example of this is the determination of a volume of a specific organ or part of an organ (for example the volume of a heart chamber). For this the cross section area of the examination subject (for example of the heart chamber) is respectively determined (as an evaluation result of the individual measurements) in the acquired slices, and the cross section area is respectively multiplied by a slice thickness or the slice interval. The volume slices that are obtained with this are then totaled up in order to obtain the total volume as an overall evaluation result. Another example is the creation of an enrichment curve, for which multiple individual measurements are implemented with a defined time interval in order to monitor the enrichment or depletion of a contrast agent in a defined tissue region of interest. Since the overall evaluation result depends on the evaluation results of a plurality of individual measurements which all have unavoidable measurement errors, the overall evaluation result is often plagued with a not inconsiderable uncertainty.